Yeah, i hear a lot of people saying they like the extra power of the bigger bike, but with bigger your looking a more fuel, more tire wear, more chain wear etc etc and buying a 250 just to spend the money on a bigger piston seems little strange to me, just buy the bigger bike..
I loved my cb1000r but it had more power than i ever needed even tho it was great fun and i would of happly got a wr250r (if i could of found a good one at the time) instead of my wr450f. It really is amazing how good modern 250's are and where they can go.

There is always going to be a compermise with a dual sport but when i am in really ruff stuff (or just trying to do a U turn on a tight track) and i'm picking up my bike plus the misses bike i want the lightest easiest bike for that time.
If the bike is only good for 80-90% of ur riding and if that other 10% is shit because the bike is to big / heavy etc your gona be yelling or sorts of things at the bike and yourself for buying the bike. It's those times you'll be wishing for something else. You dont want to come out of a great trail section just say "I'm never doing that again" cause of the bike.

My last ride on my wr450f and the misses on her xt250, i dropped my bike twice (having fun, going little silly of course) but she didn't drop her bike once and still went where i did, and she loved it.
In the past when the bike wasn't set up right, wrong tires, high seat etc she was hating how hard it was, but now right bike and right set up she is loving it.
Bigger isn't always better, sometimes its just bigger and harder, find something that fits you

Another thing, we once had to go off a very narrow track to get around an idiot in a broken down ute on a really rough track. I rode my wife's xt250 around through very very slippery bush over branches etc and I had traction all the way around and back onto the track, when I tried to get the 450 around it just kept slipping and found it really hand, even though i was very careful with the clutch and throttle. The extra power to the rear wheel made it much much harder to get traction, but there was also a really narley rocky up hill where both bikes were sliding all over the place and I just twitted the throttle and up she went no probs